Impact of thymine glycol damage on DNA duplex energetics: Correlations with lesion-induced biochemical and structural consequences

The magnitude and nature of lesion-induced energetic perturbations empirically correlate with mutagenicity/cytotoxicity profiles and can be predictive of lesion outcomes during polymerase-mediated replication in vitro. In this study, we assess the sequence and counterbase-dependent energetic impact of the Thymine glycol (T-g) lesion on a family of deoxyoligonucleotide duplexes. T-g damage arises from thymine and methyl-cytosine exposure to oxidizing agents or radiation-generated free-radicals. The T-g lesion blocks polymerase-mediated DNA replication in vitro and the unrepaired site elicits cytotoxic lethal consequences in vivo. Our combined calorimetric and spectroscopic characterization correlates T-g-induced energetic perturbations with biological and structural properties. Specifically, we incorporate a 5R-T-g isomer centered within the tridecanucleotide sequence 5-GCGTACXCATGCG-3 (X=T-g or T) which is hybridized with the corresponding complementary sequence 5-CGCATGNGTACGC-3 (N=A, G, T, C) to generate families of T-g-damaged (TgN) and lesion-free (TN) duplexes. We demonstrate that the magnitude and nature of the T-g destabilizing impact is dependent on counterbase identity (i.e., A approximate to G